One of the greatest problems facing wireless network operators is the need to serve large numbers of customers with varying needs using the infrastructure available to them. Operators of wireless networks and, indeed, most systems serving large numbers of customers, have long observed that loads nearing or exceeding the capacity of a network typically result not from the average demand presented by the users, but from peak demand resulting from simultaneous requests for service from a relatively large proportion of their user population.
Wireless networks use a number of techniques to manage their peak loads, and one mechanism that can be used as the danger of congestion increases is the temporary denial of service to various users. A base station, such as an eNodeB may broadcast signals indicating that particular users are to be excluded from making connection request. For example, the 3GPP defines standards for access class barring (ACB), in which each UE is a member of one or more access classes and User equipments (UEs) may be configured to recognize data broadcast by an eNodeB excluding their access class. 3GPP technical specification 22.011 V10.3.0 recognizes 16 access classes. Every UE is a member of one of the classes 0-9, and the classes 11-15 are reserved for UEs belonging to special categories, such as public utilities or emergency service providers. Each UE belonging to the classes 11-15 is also a member of one of the classes 0-9.
When the network needs to control the number of UEs accessing the network, it broadcasts a message indicating the current barring rate commonly applicable for classes 0-9 and a flag designating barred or unbarred status for each of classes 11-15. When a UE in one of classes 0-9 needs access to the network, it draws a random number and compares it to the current barring rate. An access attempt is allowed or not based on the comparison. If the access attempt is not allowed, further attempts are barred for a time period that is calculated based on the mean duration of access control provided by the network and the random number drawn by the UE.
The 3G Partnership Project is also discussing Extended Access Barring (EAB), which would exclude devices subject to EAB under circumstances in which other devices would be unaffected, or for timer periods longer than those applicable to devices subject to ACB.
Substantial numbers of devices that are more or less delay tolerant exist in the service areas of wireless networks. A relatively new class of users, that is, machine type communication (MTC) devices, exist in large numbers throughout the service areas of wireless networks. Many MTC devices monitor significant events such as earthquakes or other natural disasters, and the occurrence of such an event is likely to trigger activity by a great many MTC devices, which will record data and transmit the data to a host. Earthquake monitoring devices, for example, might detect and record earthquake forces and then request network service to transmit the data to a host, with the host eventually performing analysis of the data received from MTC devices distributed throughout the region affected by the earthquake. Such MTC devices typically require service for a short duration and most may not actually need service at the exact time the event occurs. However, it is also true that MTC devices do not have awareness of other demands on the network and the communication necessary to give them that information would impose an unnecessary load on the network.
Many events that would trigger requests for service by MTC devices would also give rise to more urgent demands for service, such as by emergency responders and persons requiring assistance. Network operators wish to insure that service will be available to persons having urgent need and, indeed, to ordinary non-urgent usage to the extent possible, without needing to contend with an excessive load caused by the sudden requests for service of possibly huge numbers of MTC devices seeking to upload data to a host, particularly when the devices do not even need to upload their data at any particular time.
Therefore, protocols for relatively extended denial of service are being developed. The 3GPP has agreed that if the core network (CN) is overloaded, an eNodeB associated with the core network can set an extended wait timer based on a “delay tolerant access” parameter of the RRC establishment cause, so that a UE that is to be subjected to an extended wait time, such as a delay tolerant UE, may be barred from access reattempts for a longer time period than is typical in the case of ordinary access class barring. Such a delay period may be, for example, up to 30 minutes.
Discussions are underway for the development of protocols for such extended denial of service. Such protocols are being referred to as extended access barring, or EAB.
According to 3GPP technical specification (TS) 22.011 v10.3, EAB has the following requirements:                A network may broadcast EAB information.        EAB information shall define whether EAB applies to UEs within one of the following categories:                    a) UEs that are configured for EAB;            b) UEs that are configured for EAB and are neither in their HPLMN nor in a PLMN that is equivalent to it;            c) UEs that are configured for EAB and are neither in the PLMN listed as most preferred PLMN of the country where the UE is roaming in the operator-defined PLMN selector list on the SIM/USIM, nor in their HPLMN nor in a PLMN that is equivalent to their HPLMN                        If a UE that is configured for EAB initiates an emergency call or is a member of an Access Class in the range 11-15 and according to clause 4.3.1 that Access Class is permitted by the network, then the UE shall ignore any EAB information that is broadcast by the network.        A UE configured for EAB shall use its allocated Access Class(es), as defined in sub-clause 4.2, when evaluating the EAB information that is broadcast by the network, in order to determine if its access to the network is barred.        If the network is not broadcasting the EAB information, the UE shall be subject to access barring as described in clause 4.3.1        If the EAB information that is broadcast by the network does not bar the UE, the UE shall be subject to access barring as described in clause 4.3.1.        
If the UE will not be subject to EAB, the UE should apply normal access class barring based on its access class. In addition, if no EAB information is being broadcast, such as on the broadcast control channel (BCCH), the UE should apply normal access class barring.
Access class is applied based on the call type in evolved UMTS terrestrial radio access network (E-UTRAN) or on the RRC establishment cause in UTRAN. In E-UTRAN, the non-access stratum (NAS) indicates the call type and the RRC establishment cause to the access stratum (AS), and in UTRAN, the NAS indicates the RRC establishment cause to the AS.
The interface between the NAS and the AS is a UE internal interface, and standardized mapping is applied between a specific NAS signalling procedure. The call type and RRC establishment provided by NAS to the AS is standardized in normative annexes in 3GPP technical specifications 24.301 (Annex D) and 24.008 (Annex L). The following is an example extracted from Annex D.
TABLE D.1.1Mapping of NAS procedure to establishment cause and call typeNASproce-RRC establishment causedure(according 3GPP TS 36.331 [22])Call typeAttachIf an ATTACH REQUEST has EPS attach type“originatingnot set to “EPS emergency attach”, the RRCsignalling”establishment cause shall be set to MOsignalling except when the UE initiates attachprocedure to establish emergency bearerservices. (See Note 1)If an ATTACH REQUEST has EPS attach type“originatingnot set to “EPS emergency attach” and UE issignalling”configured for NAS signalling low priority,the RRC establishment cause shall be set toDelay tolerant. (See Note 1)If an ATTACH REQUEST has EPS attach type“emergencyset to “EPS emergency attach” or if the ATTACHcalls”REQUEST has EPS attach type not set to “EPSemergency attach” but the UE initiates theattach procedure on receiving request fromupper layer to establish emergency bearerservices, the RRC establishment cause shallbe set to Emergency call. (See Note 1)Note 1:For these NAS procedures initiated by UEs of access class 12, 13 or 14 in their home country, the RRC establishment cause will be set to “High priority access AC 11-15”. For this purpose the home country is defined as the country of the MCC part of the IMSI, see 3GPP TS 22.011 [1A].For these NAS procedures initiated by UE of access class 11 or 15 in their HPLMN (if the EHPLMN list is not present or is empty) or EHPLMN (if the EHPLMN list is present), the RRC establishment cause will be set to “High priority access AC 11-15”.Note 2:This is not applicable for mobile terminating 1xCS fallback.